Abstract : Optical intensity measurements are shown to be effective for detecting fluxes of low energy (1 to 4 MeV) protons in the polar cap. Energies calculated from N2(+) IN optical intensities showed close agreement with energies calculated from particle differential energy spectra for two Solar Particle Events (SPE) with markedly different energy spectra. Satellite measurements showed the 2 Nov 1969 SPE had fewer 2-MeV protons than the 7 Nov 1969 SPE but had 100 times more protons with energies greater than 10 MeV. The fact that optical emissions are produced by large fluxes of low energy protons is contrasted with riometer measurements, which have been shown to be related to fluxes of protons with energies greater than 5 to 10 MeV. (Author)